I had a similar issue with my aging canary.
She can fly down from her cage and happily potter about on the floor but hasn’t the strength to fly back up to it.
When she was in her vision cage, I would just lift the cage down to the floor and she’d pop back inside, but now she’s in a large single flight cage and that isn’t an option.
What I found works with her though, is to place an empty clothes airer beside the cage, that she can use it to break the journey back upwards, into a few shorter jumps.
You could try something similar - If you can bring the cage to them then do. If it’s too large, then providing they can still clearly ‘see’ what they’re aiming for, try to place an airer (or dining chair or anything of midway height) nearby, in order to split the leap upwards into more manageable heights.
Alternatively, you could try adding a spiral boing, from the cage down to the floor.
I’d only try this at a time when you have a lot of free time to allow them to work it out for themselves. If their previous clipping means that they’re gaining no height at all, and their cage is too big to move, then I’d just wait for more growth to occur.